The present embodiments relate diagnostics for programmable logic controllers (PLCs).
PLCs control automated processes, such as controlling operations in a factory. A PLC connects with one or more loads, such as motors, actuators, and/or sensors. The connection allows control of the load by the PLC. However, the connection and/or the load may fail. For example, a wire becomes disconnected or shorted to ground or a high voltage.
To deal with possible connection problems, self-contained diagnostic circuitry is included in the PLC. Self-contained diagnostic circuitry is provided for each output or possible connection. However, the additional circuitry may be expensive to implement for multiple channel PLCs, both in cost and printed wiring board (PWB) real estate.
One way to limit the diagnostic circuitry is to use the output driver itself. For example, a short-to-ground or overload is to be detected. When the output driver is in an “on” state, thermal overload of the driver may occur due to the overload. The thermal overload shuts down the driver for a sufficient time to cool (e.g., a few seconds). If thermal overload occurs every time the driver is turned on, then the overload is detected. However, this may overly stress the output driver.